Sophisticated and robust numerical modeling is essential to developing a good understanding
of complex physical and chemical phenomena in the subsurface. In this chapter we provide a general
overview of NUFT (Nonisothermal Unsaturated-saturated Flow and Transport) code, which is a highly
flexible computer software package for modeling multiphase, multi-component heat and mass flow
and reactive transport in unsaturated and saturated porous media. An integrated finite difference method
is used for numerical discretization. Several mathematical models are implemented in order to address
various flow and reactive transport processes in porous media. The governing equations for each submodel
are solved by implicit time-integration. In particular a globally implicit approach is employed to
solve transport and reaction equations simultaneously. The code is designed based on object-oriented
principles, and equipped with efficient solvers and massively parallel computation capability. We
present two examples involving reactive transport modeling to demonstrate capabilities of the code.
Keywords: NUFT, multiphase and multicomponent flow, reactive transport, porous media, numerical model.
